Switch pins between GPIO and JTAG (gpio_jtag)

Compatibility: Eagle 50, 50E, 100

This example demonstrates changing the JTAG pins into GPIOs, along with a mechanism to revert them to JTAG pins. When first run, the pins remain in JTAG mode. Pressing the select push button
will toggle the pins between JTAG mode and GPIO mode. Because there is no debouncing of the push button (either in hardware or software), a button press will occasionally result in more than
one mode change.

In this example, all five pins (PB7, PC0, PC1, PC2, and PC3) are switched, though the more typical use would be to change PB7 into a GPIO.